Merge pull request #390 from NguyenSiTrung/main

feat(amp): add model mapping support for routing unavailable models to alternatives

README.md

@@ -56,6 +56,7 @@ CLIProxyAPI includes integrated support for [Amp CLI](https://ampcode.com) and A
 - Provider route aliases for Amp's API patterns (`/api/provider/{provider}/v1...`)
 - Management proxy for OAuth authentication and account features
 - Smart model fallback with automatic routing
+- **Model mapping** to route unavailable models to alternatives (e.g., `claude-opus-4.5` → `claude-sonnet-4`)
 - Security-first design with localhost-only management endpoints
 
 **→ [Complete Amp CLI Integration Guide](docs/amp-cli-integration.md)**

config.example.yaml

@@ -55,6 +55,28 @@ quota-exceeded:
 # When true, enable authentication for the WebSocket API (/v1/ws).
 ws-auth: false
 
+# Amp CLI Integration
+# Configure upstream URL for Amp CLI OAuth and management features
+#amp-upstream-url: "https://ampcode.com"
+
+# Optional: Override API key for Amp upstream (otherwise uses env or file)
+#amp-upstream-api-key: ""
+
+# Restrict Amp management routes (/api/auth, /api/user, etc.) to localhost only (recommended)
+#amp-restrict-management-to-localhost: true
+
+# Amp Model Mappings
+# Route unavailable Amp models to alternative models available in your local proxy.
+# Useful when Amp CLI requests models you don't have access to (e.g., Claude Opus 4.5)
+# but you have a similar model available (e.g., Claude Sonnet 4).
+#amp-model-mappings:
+#  - from: "claude-opus-4.5"       # Model requested by Amp CLI
+#    to: "claude-sonnet-4"         # Route to this available model instead
+#  - from: "gpt-5"
+#    to: "gemini-2.5-pro"
+#  - from: "claude-3-opus-20240229"
+#    to: "claude-3-5-sonnet-20241022"
+
 # Gemini API keys (preferred)
 #gemini-api-key:
 #  - api-key: "AIzaSy...01"

docs/amp-cli-integration.md

@@ -8,6 +8,7 @@ This guide explains how to use CLIProxyAPI with Amp CLI and Amp IDE extensions,
   - [Which Providers Should You Authenticate?](#which-providers-should-you-authenticate)
 - [Architecture](#architecture)
 - [Configuration](#configuration)
+  - [Model Mapping Configuration](#model-mapping-configuration)
 - [Setup](#setup)
 - [Usage](#usage)
 - [Troubleshooting](#troubleshooting)
@@ -21,6 +22,7 @@ The Amp CLI integration adds specialized routing to support Amp's API patterns w
 - **Provider route aliases**: Maps Amp's `/api/provider/{provider}/v1...` patterns to CLIProxyAPI handlers
 - **Management proxy**: Forwards OAuth and account management requests to Amp's control plane
 - **Smart fallback**: Automatically routes unconfigured models to ampcode.com
+- **Model mapping**: Route unavailable models to alternatives you have access to (e.g., `claude-opus-4.5` → `claude-sonnet-4`)
 - **Secret management**: Configurable precedence (config > env > file) with 5-minute caching
 - **Security-first**: Management routes restricted to localhost by default
 - **Automatic gzip handling**: Decompresses responses from Amp upstream
@@ -75,7 +77,10 @@ Amp CLI/IDE
   │   ↓
   │   ├─ Model configured locally?
   │   │   YES → Use local OAuth tokens (OpenAI/Claude/Gemini handlers)
-  │   │   NO  → Forward to ampcode.com (reverse proxy)
+  │   │   NO  ↓
+  │   │       ├─ Model mapping configured?
+  │   │       │   YES → Rewrite model → Use local handler (free)
+  │   │       │   NO  → Forward to ampcode.com (uses Amp credits)
   │   ↓
   │   Response
   │
@@ -115,6 +120,49 @@ amp-upstream-url: "https://ampcode.com"
 amp-restrict-management-to-localhost: true
 ```
 
+### Model Mapping Configuration
+
+When Amp CLI requests a model that you don't have access to, you can configure mappings to route those requests to alternative models that you DO have available. This avoids consuming Amp credits for models you could handle locally.
+
+```yaml
+# Route unavailable models to alternatives
+amp-model-mappings:
+  # Example: Route Claude Opus 4.5 requests to Claude Sonnet 4
+  - from: "claude-opus-4.5"
+    to: "claude-sonnet-4"
+  
+  # Example: Route GPT-5 requests to Gemini 2.5 Pro
+  - from: "gpt-5"
+    to: "gemini-2.5-pro"
+  
+  # Example: Map older model names to newer versions
+  - from: "claude-3-opus-20240229"
+    to: "claude-3-5-sonnet-20241022"
+```
+
+**How it works:**
+
+1. Amp CLI requests a model (e.g., `claude-opus-4.5`)
+2. CLIProxyAPI checks if a local provider is available for that model
+3. If not available, it checks the model mappings
+4. If a mapping exists, the request is rewritten to use the target model
+5. The request is then handled locally (free, using your OAuth subscription)
+
+**Benefits:**
+- **Save Amp credits**: Use your local subscriptions instead of forwarding to ampcode.com
+- **Hot-reload**: Mappings can be updated without restarting the proxy
+- **Structured logging**: Clear logs show when mappings are applied
+
+**Routing Decision Logs:**
+
+The proxy logs each routing decision with structured fields:
+
+```
+[AMP] Using local provider for model: gemini-2.5-pro          # Local provider (free)
+[AMP] Model mapped: claude-opus-4.5 -> claude-sonnet-4        # Mapping applied (free)
+[AMP] Forwarding to ampcode.com (uses Amp credits) - model_id: gpt-5  # Fallback (costs credits)
+```
+
 ### Secret Resolution Precedence
 
 The Amp module resolves API keys using this precedence order:
@@ -301,11 +349,14 @@ When Amp requests a model:
 
 1. **Check local configuration**: Does CLIProxyAPI have OAuth tokens for this model's provider?
 2. **If YES**: Route to local handler (use your OAuth subscription)
-3. **If NO**: Forward to ampcode.com (use Amp's default routing)
+3. **If NO**: Check if a model mapping exists
+4. **If mapping exists**: Rewrite request to mapped model → Route to local handler (free)
+5. **If no mapping**: Forward to ampcode.com (uses Amp credits)
 
 This enables seamless mixed usage:
 - Models you've configured (Gemini, ChatGPT, Claude) → Your OAuth subscriptions
-- Models you haven't configured → Amp's default providers
+- Models with mappings configured → Routed to alternative local models (free)
+- Models you haven't configured and have no mapping → Amp's default providers (uses credits)
 
 ### Example API Calls
 

internal/api/modules/amp/amp.go

@@ -23,11 +23,13 @@ type Option func(*AmpModule)
 //   - Reverse proxy to Amp control plane for OAuth/management
 //   - Provider-specific route aliases (/api/provider/{provider}/...)
 //   - Automatic gzip decompression for misconfigured upstreams
+//   - Model mapping for routing unavailable models to alternatives
 type AmpModule struct {
 	secretSource    SecretSource
 	proxy           *httputil.ReverseProxy
 	accessManager   *sdkaccess.Manager
 	authMiddleware_ gin.HandlerFunc
+	modelMapper     *DefaultModelMapper
 	enabled         bool
 	registerOnce    sync.Once
 }
@@ -101,6 +103,9 @@ func (m *AmpModule) Register(ctx modules.Context) error {
 	// Use registerOnce to ensure routes are only registered once
 	var regErr error
 	m.registerOnce.Do(func() {
+		// Initialize model mapper from config (for routing unavailable models to alternatives)
+		m.modelMapper = NewModelMapper(ctx.Config.AmpModelMappings)
+
 		// Always register provider aliases - these work without an upstream
 		m.registerProviderAliases(ctx.Engine, ctx.BaseHandler, auth)
 
@@ -159,8 +164,16 @@ func (m *AmpModule) getAuthMiddleware(ctx modules.Context) gin.HandlerFunc {
 // OnConfigUpdated handles configuration updates.
 // Currently requires restart for URL changes (could be enhanced for dynamic updates).
 func (m *AmpModule) OnConfigUpdated(cfg *config.Config) error {
+	// Update model mappings (hot-reload supported)
+	if m.modelMapper != nil {
+		log.Infof("amp config updated: reloading %d model mapping(s)", len(cfg.AmpModelMappings))
+		m.modelMapper.UpdateMappings(cfg.AmpModelMappings)
+	} else {
+		log.Warnf("amp model mapper not initialized, skipping model mapping update")
+	}
+
 	if !m.enabled {
-		log.Debug("Amp routing not enabled, skipping config update")
+		log.Debug("Amp routing not enabled, skipping other config updates")
 		return nil
 	}
 
@@ -181,3 +194,8 @@ func (m *AmpModule) OnConfigUpdated(cfg *config.Config) error {
 	log.Debug("Amp config updated (restart required for URL changes)")
 	return nil
 }
+
+// GetModelMapper returns the model mapper instance (for testing/debugging).
+func (m *AmpModule) GetModelMapper() *DefaultModelMapper {
+	return m.modelMapper
+}

internal/api/modules/amp/fallback_handlers.go

@@ -6,16 +6,75 @@ import (
 	"io"
 	"net/http/httputil"
 	"strings"
+	"time"
 
 	"github.com/gin-gonic/gin"
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/util"
 	log "github.com/sirupsen/logrus"
 )
 
+// AmpRouteType represents the type of routing decision made for an Amp request
+type AmpRouteType string
+
+const (
+	// RouteTypeLocalProvider indicates the request is handled by a local OAuth provider (free)
+	RouteTypeLocalProvider AmpRouteType = "LOCAL_PROVIDER"
+	// RouteTypeModelMapping indicates the request was remapped to another available model (free)
+	RouteTypeModelMapping AmpRouteType = "MODEL_MAPPING"
+	// RouteTypeAmpCredits indicates the request is forwarded to ampcode.com (uses Amp credits)
+	RouteTypeAmpCredits AmpRouteType = "AMP_CREDITS"
+	// RouteTypeNoProvider indicates no provider or fallback available
+	RouteTypeNoProvider AmpRouteType = "NO_PROVIDER"
+)
+
+// logAmpRouting logs the routing decision for an Amp request with structured fields
+func logAmpRouting(routeType AmpRouteType, requestedModel, resolvedModel, provider, path string) {
+	fields := log.Fields{
+		"component":       "amp-routing",
+		"route_type":      string(routeType),
+		"requested_model": requestedModel,
+		"path":            path,
+		"timestamp":       time.Now().Format(time.RFC3339),
+	}
+
+	if resolvedModel != "" && resolvedModel != requestedModel {
+		fields["resolved_model"] = resolvedModel
+	}
+	if provider != "" {
+		fields["provider"] = provider
+	}
+
+	switch routeType {
+	case RouteTypeLocalProvider:
+		fields["cost"] = "free"
+		fields["source"] = "local_oauth"
+		log.WithFields(fields).Infof("[AMP] Using local provider for model: %s", requestedModel)
+
+	case RouteTypeModelMapping:
+		fields["cost"] = "free"
+		fields["source"] = "local_oauth"
+		fields["mapping"] = requestedModel + " -> " + resolvedModel
+		log.WithFields(fields).Infof("[AMP] Model mapped: %s -> %s", requestedModel, resolvedModel)
+
+	case RouteTypeAmpCredits:
+		fields["cost"] = "amp_credits"
+		fields["source"] = "ampcode.com"
+		fields["model_id"] = requestedModel // Explicit model_id for easy config reference
+		log.WithFields(fields).Warnf("[AMP] Forwarding to ampcode.com (uses Amp credits) - model_id: %s | To use local proxy, add to config: amp-model-mappings: [{from: \"%s\", to: \"<your-local-model>\"}]", requestedModel, requestedModel)
+
+	case RouteTypeNoProvider:
+		fields["cost"] = "none"
+		fields["source"] = "error"
+		fields["model_id"] = requestedModel // Explicit model_id for easy config reference
+		log.WithFields(fields).Warnf("[AMP] No provider available for model_id: %s", requestedModel)
+	}
+}
+
 // FallbackHandler wraps a standard handler with fallback logic to ampcode.com
 // when the model's provider is not available in CLIProxyAPI
 type FallbackHandler struct {
-	getProxy func() *httputil.ReverseProxy
+	getProxy    func() *httputil.ReverseProxy
+	modelMapper ModelMapper
 }
 
 // NewFallbackHandler creates a new fallback handler wrapper
@@ -26,10 +85,25 @@ func NewFallbackHandler(getProxy func() *httputil.ReverseProxy) *FallbackHandler
 	}
 }
 
+// NewFallbackHandlerWithMapper creates a new fallback handler with model mapping support
+func NewFallbackHandlerWithMapper(getProxy func() *httputil.ReverseProxy, mapper ModelMapper) *FallbackHandler {
+	return &FallbackHandler{
+		getProxy:    getProxy,
+		modelMapper: mapper,
+	}
+}
+
+// SetModelMapper sets the model mapper for this handler (allows late binding)
+func (fh *FallbackHandler) SetModelMapper(mapper ModelMapper) {
+	fh.modelMapper = mapper
+}
+
 // WrapHandler wraps a gin.HandlerFunc with fallback logic
 // If the model's provider is not configured in CLIProxyAPI, it forwards to ampcode.com
 func (fh *FallbackHandler) WrapHandler(handler gin.HandlerFunc) gin.HandlerFunc {
 	return func(c *gin.Context) {
+		requestPath := c.Request.URL.Path
+
 		// Read the request body to extract the model name
 		bodyBytes, err := io.ReadAll(c.Request.Body)
 		if err != nil {
@@ -55,12 +129,33 @@ func (fh *FallbackHandler) WrapHandler(handler gin.HandlerFunc) gin.HandlerFunc
 		// Check if we have providers for this model
 		providers := util.GetProviderName(normalizedModel)
 
+		// Track resolved model for logging (may change if mapping is applied)
+		resolvedModel := normalizedModel
+		usedMapping := false
+
 		if len(providers) == 0 {
-			// No providers configured - check if we have a proxy for fallback
+			// No providers configured - check if we have a model mapping
+			if fh.modelMapper != nil {
+				if mappedModel := fh.modelMapper.MapModel(normalizedModel); mappedModel != "" {
+					// Mapping found - rewrite the model in request body
+					bodyBytes = rewriteModelInBody(bodyBytes, mappedModel)
+					c.Request.Body = io.NopCloser(bytes.NewReader(bodyBytes))
+					resolvedModel = mappedModel
+					usedMapping = true
+
+					// Get providers for the mapped model
+					providers = util.GetProviderName(mappedModel)
+
+					// Continue to handler with remapped model
+					goto handleRequest
+				}
+			}
+
+			// No mapping found - check if we have a proxy for fallback
 			proxy := fh.getProxy()
 			if proxy != nil {
-				// Fallback to ampcode.com
-				log.Infof("amp fallback: model %s has no configured provider, forwarding to ampcode.com", modelName)
+				// Log: Forwarding to ampcode.com (uses Amp credits)
+				logAmpRouting(RouteTypeAmpCredits, modelName, "", "", requestPath)
 
 				// Restore body again for the proxy
 				c.Request.Body = io.NopCloser(bytes.NewReader(bodyBytes))
@@ -71,7 +166,23 @@ func (fh *FallbackHandler) WrapHandler(handler gin.HandlerFunc) gin.HandlerFunc
 			}
 
 			// No proxy available, let the normal handler return the error
-			log.Debugf("amp fallback: model %s has no configured provider and no proxy available", modelName)
+			logAmpRouting(RouteTypeNoProvider, modelName, "", "", requestPath)
+		}
+
+	handleRequest:
+
+		// Log the routing decision
+		providerName := ""
+		if len(providers) > 0 {
+			providerName = providers[0]
+		}
+
+		if usedMapping {
+			// Log: Model was mapped to another model
+			logAmpRouting(RouteTypeModelMapping, modelName, resolvedModel, providerName, requestPath)
+		} else if len(providers) > 0 {
+			// Log: Using local provider (free)
+			logAmpRouting(RouteTypeLocalProvider, modelName, resolvedModel, providerName, requestPath)
 		}
 
 		// Providers available or no proxy for fallback, restore body and use normal handler
@@ -91,6 +202,27 @@ func (fh *FallbackHandler) WrapHandler(handler gin.HandlerFunc) gin.HandlerFunc
 	}
 }
 
+// rewriteModelInBody replaces the model name in a JSON request body
+func rewriteModelInBody(body []byte, newModel string) []byte {
+	var payload map[string]interface{}
+	if err := json.Unmarshal(body, &payload); err != nil {
+		log.Warnf("amp model mapping: failed to parse body for rewrite: %v", err)
+		return body
+	}
+
+	if _, exists := payload["model"]; exists {
+		payload["model"] = newModel
+		newBody, err := json.Marshal(payload)
+		if err != nil {
+			log.Warnf("amp model mapping: failed to marshal rewritten body: %v", err)
+			return body
+		}
+		return newBody
+	}
+
+	return body
+}
+
 // extractModelFromRequest attempts to extract the model name from various request formats
 func extractModelFromRequest(body []byte, c *gin.Context) string {
 	// First try to parse from JSON body (OpenAI, Claude, etc.)

internal/api/modules/amp/model_mapping.go

@@ -0,0 +1,113 @@
+// Package amp provides model mapping functionality for routing Amp CLI requests
+// to alternative models when the requested model is not available locally.
+package amp
+
+import (
+	"strings"
+	"sync"
+
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/util"
+	log "github.com/sirupsen/logrus"
+)
+
+// ModelMapper provides model name mapping/aliasing for Amp CLI requests.
+// When an Amp request comes in for a model that isn't available locally,
+// this mapper can redirect it to an alternative model that IS available.
+type ModelMapper interface {
+	// MapModel returns the target model name if a mapping exists and the target
+	// model has available providers. Returns empty string if no mapping applies.
+	MapModel(requestedModel string) string
+
+	// UpdateMappings refreshes the mapping configuration (for hot-reload).
+	UpdateMappings(mappings []config.AmpModelMapping)
+}
+
+// DefaultModelMapper implements ModelMapper with thread-safe mapping storage.
+type DefaultModelMapper struct {
+	mu       sync.RWMutex
+	mappings map[string]string // from -> to (normalized lowercase keys)
+}
+
+// NewModelMapper creates a new model mapper with the given initial mappings.
+func NewModelMapper(mappings []config.AmpModelMapping) *DefaultModelMapper {
+	m := &DefaultModelMapper{
+		mappings: make(map[string]string),
+	}
+	m.UpdateMappings(mappings)
+	return m
+}
+
+// MapModel checks if a mapping exists for the requested model and if the
+// target model has available local providers. Returns the mapped model name
+// or empty string if no valid mapping exists.
+func (m *DefaultModelMapper) MapModel(requestedModel string) string {
+	if requestedModel == "" {
+		return ""
+	}
+
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	// Normalize the requested model for lookup
+	normalizedRequest := strings.ToLower(strings.TrimSpace(requestedModel))
+
+	// Check for direct mapping
+	targetModel, exists := m.mappings[normalizedRequest]
+	if !exists {
+		return ""
+	}
+
+	// Verify target model has available providers
+	providers := util.GetProviderName(targetModel)
+	if len(providers) == 0 {
+		log.Debugf("amp model mapping: target model %s has no available providers, skipping mapping", targetModel)
+		return ""
+	}
+
+	// Note: Detailed routing log is handled by logAmpRouting in fallback_handlers.go
+	log.Debugf("amp model mapping: resolved %s -> %s", requestedModel, targetModel)
+	return targetModel
+}
+
+// UpdateMappings refreshes the mapping configuration from config.
+// This is called during initialization and on config hot-reload.
+func (m *DefaultModelMapper) UpdateMappings(mappings []config.AmpModelMapping) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	// Clear and rebuild mappings
+	m.mappings = make(map[string]string, len(mappings))
+
+	for _, mapping := range mappings {
+		from := strings.TrimSpace(mapping.From)
+		to := strings.TrimSpace(mapping.To)
+
+		if from == "" || to == "" {
+			log.Warnf("amp model mapping: skipping invalid mapping (from=%q, to=%q)", from, to)
+			continue
+		}
+
+		// Store with normalized lowercase key for case-insensitive lookup
+		normalizedFrom := strings.ToLower(from)
+		m.mappings[normalizedFrom] = to
+
+		log.Debugf("amp model mapping registered: %s -> %s", from, to)
+	}
+
+	if len(m.mappings) > 0 {
+		log.Infof("amp model mapping: loaded %d mapping(s)", len(m.mappings))
+	}
+}
+
+// GetMappings returns a copy of current mappings (for debugging/status).
+func (m *DefaultModelMapper) GetMappings() map[string]string {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	result := make(map[string]string, len(m.mappings))
+	for k, v := range m.mappings {
+		result[k] = v
+	}
+	return result
+}

internal/api/modules/amp/model_mapping_test.go

@@ -0,0 +1,186 @@
+package amp
+
+import (
+	"testing"
+
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/registry"
+)
+
+func TestNewModelMapper(t *testing.T) {
+	mappings := []config.AmpModelMapping{
+		{From: "claude-opus-4.5", To: "claude-sonnet-4"},
+		{From: "gpt-5", To: "gemini-2.5-pro"},
+	}
+
+	mapper := NewModelMapper(mappings)
+	if mapper == nil {
+		t.Fatal("Expected non-nil mapper")
+	}
+
+	result := mapper.GetMappings()
+	if len(result) != 2 {
+		t.Errorf("Expected 2 mappings, got %d", len(result))
+	}
+}
+
+func TestNewModelMapper_Empty(t *testing.T) {
+	mapper := NewModelMapper(nil)
+	if mapper == nil {
+		t.Fatal("Expected non-nil mapper")
+	}
+
+	result := mapper.GetMappings()
+	if len(result) != 0 {
+		t.Errorf("Expected 0 mappings, got %d", len(result))
+	}
+}
+
+func TestModelMapper_MapModel_NoProvider(t *testing.T) {
+	mappings := []config.AmpModelMapping{
+		{From: "claude-opus-4.5", To: "claude-sonnet-4"},
+	}
+
+	mapper := NewModelMapper(mappings)
+
+	// Without a registered provider for the target, mapping should return empty
+	result := mapper.MapModel("claude-opus-4.5")
+	if result != "" {
+		t.Errorf("Expected empty result when target has no provider, got %s", result)
+	}
+}
+
+func TestModelMapper_MapModel_WithProvider(t *testing.T) {
+	// Register a mock provider for the target model
+	reg := registry.GetGlobalRegistry()
+	reg.RegisterClient("test-client", "claude", []*registry.ModelInfo{
+		{ID: "claude-sonnet-4", OwnedBy: "anthropic", Type: "claude"},
+	})
+	defer reg.UnregisterClient("test-client")
+
+	mappings := []config.AmpModelMapping{
+		{From: "claude-opus-4.5", To: "claude-sonnet-4"},
+	}
+
+	mapper := NewModelMapper(mappings)
+
+	// With a registered provider, mapping should work
+	result := mapper.MapModel("claude-opus-4.5")
+	if result != "claude-sonnet-4" {
+		t.Errorf("Expected claude-sonnet-4, got %s", result)
+	}
+}
+
+func TestModelMapper_MapModel_CaseInsensitive(t *testing.T) {
+	reg := registry.GetGlobalRegistry()
+	reg.RegisterClient("test-client2", "claude", []*registry.ModelInfo{
+		{ID: "claude-sonnet-4", OwnedBy: "anthropic", Type: "claude"},
+	})
+	defer reg.UnregisterClient("test-client2")
+
+	mappings := []config.AmpModelMapping{
+		{From: "Claude-Opus-4.5", To: "claude-sonnet-4"},
+	}
+
+	mapper := NewModelMapper(mappings)
+
+	// Should match case-insensitively
+	result := mapper.MapModel("claude-opus-4.5")
+	if result != "claude-sonnet-4" {
+		t.Errorf("Expected claude-sonnet-4, got %s", result)
+	}
+}
+
+func TestModelMapper_MapModel_NotFound(t *testing.T) {
+	mappings := []config.AmpModelMapping{
+		{From: "claude-opus-4.5", To: "claude-sonnet-4"},
+	}
+
+	mapper := NewModelMapper(mappings)
+
+	// Unknown model should return empty
+	result := mapper.MapModel("unknown-model")
+	if result != "" {
+		t.Errorf("Expected empty for unknown model, got %s", result)
+	}
+}
+
+func TestModelMapper_MapModel_EmptyInput(t *testing.T) {
+	mappings := []config.AmpModelMapping{
+		{From: "claude-opus-4.5", To: "claude-sonnet-4"},
+	}
+
+	mapper := NewModelMapper(mappings)
+
+	result := mapper.MapModel("")
+	if result != "" {
+		t.Errorf("Expected empty for empty input, got %s", result)
+	}
+}
+
+func TestModelMapper_UpdateMappings(t *testing.T) {
+	mapper := NewModelMapper(nil)
+
+	// Initially empty
+	if len(mapper.GetMappings()) != 0 {
+		t.Error("Expected 0 initial mappings")
+	}
+
+	// Update with new mappings
+	mapper.UpdateMappings([]config.AmpModelMapping{
+		{From: "model-a", To: "model-b"},
+		{From: "model-c", To: "model-d"},
+	})
+
+	result := mapper.GetMappings()
+	if len(result) != 2 {
+		t.Errorf("Expected 2 mappings after update, got %d", len(result))
+	}
+
+	// Update again should replace, not append
+	mapper.UpdateMappings([]config.AmpModelMapping{
+		{From: "model-x", To: "model-y"},
+	})
+
+	result = mapper.GetMappings()
+	if len(result) != 1 {
+		t.Errorf("Expected 1 mapping after second update, got %d", len(result))
+	}
+}
+
+func TestModelMapper_UpdateMappings_SkipsInvalid(t *testing.T) {
+	mapper := NewModelMapper(nil)
+
+	mapper.UpdateMappings([]config.AmpModelMapping{
+		{From: "", To: "model-b"},      // Invalid: empty from
+		{From: "model-a", To: ""},      // Invalid: empty to
+		{From: "  ", To: "model-b"},    // Invalid: whitespace from
+		{From: "model-c", To: "model-d"}, // Valid
+	})
+
+	result := mapper.GetMappings()
+	if len(result) != 1 {
+		t.Errorf("Expected 1 valid mapping, got %d", len(result))
+	}
+}
+
+func TestModelMapper_GetMappings_ReturnsCopy(t *testing.T) {
+	mappings := []config.AmpModelMapping{
+		{From: "model-a", To: "model-b"},
+	}
+
+	mapper := NewModelMapper(mappings)
+
+	// Get mappings and modify the returned map
+	result := mapper.GetMappings()
+	result["new-key"] = "new-value"
+
+	// Original should be unchanged
+	original := mapper.GetMappings()
+	if len(original) != 1 {
+		t.Errorf("Expected original to have 1 mapping, got %d", len(original))
+	}
+	if _, exists := original["new-key"]; exists {
+		t.Error("Original map was modified")
+	}
+}

internal/api/modules/amp/routes.go

@@ -170,9 +170,10 @@ func (m *AmpModule) registerProviderAliases(engine *gin.Engine, baseHandler *han
 
 	// Create fallback handler wrapper that forwards to ampcode.com when provider not found
 	// Uses lazy evaluation to access proxy (which is created after routes are registered)
-	fallbackHandler := NewFallbackHandler(func() *httputil.ReverseProxy {
+	// Also includes model mapping support for routing unavailable models to alternatives
+	fallbackHandler := NewFallbackHandlerWithMapper(func() *httputil.ReverseProxy {
 		return m.proxy
-	})
+	}, m.modelMapper)
 
 	// Provider-specific routes under /api/provider/:provider
 	ampProviders := engine.Group("/api/provider")

internal/api/server.go

@@ -150,6 +150,9 @@ type Server struct {
 	// management handler
 	mgmt *managementHandlers.Handler
 
+	// ampModule is the Amp routing module for model mapping hot-reload
+	ampModule *ampmodule.AmpModule
+
 	// managementRoutesRegistered tracks whether the management routes have been attached to the engine.
 	managementRoutesRegistered atomic.Bool
 	// managementRoutesEnabled controls whether management endpoints serve real handlers.
@@ -268,14 +271,14 @@ func NewServer(cfg *config.Config, authManager *auth.Manager, accessManager *sdk
 	s.setupRoutes()
 
 	// Register Amp module using V2 interface with Context
-	ampModule := ampmodule.NewLegacy(accessManager, AuthMiddleware(accessManager))
+	s.ampModule = ampmodule.NewLegacy(accessManager, AuthMiddleware(accessManager))
 	ctx := modules.Context{
 		Engine:         engine,
 		BaseHandler:    s.handlers,
 		Config:         cfg,
 		AuthMiddleware: AuthMiddleware(accessManager),
 	}
-	if err := modules.RegisterModule(ctx, ampModule); err != nil {
+	if err := modules.RegisterModule(ctx, s.ampModule); err != nil {
 		log.Errorf("Failed to register Amp module: %v", err)
 	}
 
@@ -916,6 +919,16 @@ func (s *Server) UpdateClients(cfg *config.Config) {
 		s.mgmt.SetAuthManager(s.handlers.AuthManager)
 	}
 
+	// Notify Amp module of config changes (for model mapping hot-reload)
+	if s.ampModule != nil {
+		log.Debugf("triggering amp module config update")
+		if err := s.ampModule.OnConfigUpdated(cfg); err != nil {
+			log.Errorf("failed to update Amp module config: %v", err)
+		}
+	} else {
+		log.Warnf("amp module is nil, skipping config update")
+	}
+
 	// Count client sources from configuration and auth directory
 	authFiles := util.CountAuthFiles(cfg.AuthDir)
 	geminiAPIKeyCount := len(cfg.GeminiKey)

internal/config/config.go

@@ -37,6 +37,12 @@ type Config struct {
 	// browser attacks and remote access to management endpoints. Default: true (recommended).
 	AmpRestrictManagementToLocalhost bool `yaml:"amp-restrict-management-to-localhost" json:"amp-restrict-management-to-localhost"`
 
+	// AmpModelMappings defines model name mappings for Amp CLI requests.
+	// When Amp requests a model that isn't available locally, these mappings
+	// allow routing to an alternative model that IS available.
+	// Example: Map "claude-opus-4.5" -> "claude-sonnet-4" when opus isn't available.
+	AmpModelMappings []AmpModelMapping `yaml:"amp-model-mappings" json:"amp-model-mappings"`
+
 	// AuthDir is the directory where authentication token files are stored.
 	AuthDir string `yaml:"auth-dir" json:"-"`
 
@@ -118,6 +124,18 @@ type QuotaExceeded struct {
 	SwitchPreviewModel bool `yaml:"switch-preview-model" json:"switch-preview-model"`
 }
 
+// AmpModelMapping defines a model name mapping for Amp CLI requests.
+// When Amp requests a model that isn't available locally, this mapping
+// allows routing to an alternative model that IS available.
+type AmpModelMapping struct {
+	// From is the model name that Amp CLI requests (e.g., "claude-opus-4.5").
+	From string `yaml:"from" json:"from"`
+
+	// To is the target model name to route to (e.g., "claude-sonnet-4").
+	// The target model must have available providers in the registry.
+	To string `yaml:"to" json:"to"`
+}
+
 // PayloadConfig defines default and override parameter rules applied to provider payloads.
 type PayloadConfig struct {
 	// Default defines rules that only set parameters when they are missing in the payload.

internal/watcher/watcher.go

@@ -162,12 +162,14 @@ func NewWatcher(configPath, authDir string, reloadCallback func(*config.Config))
 
 // Start begins watching the configuration file and authentication directory
 func (w *Watcher) Start(ctx context.Context) error {
-	// Watch the config file
-	if errAddConfig := w.watcher.Add(w.configPath); errAddConfig != nil {
-		log.Errorf("failed to watch config file %s: %v", w.configPath, errAddConfig)
+	// Watch the config file's parent directory instead of the file itself.
+	// This handles editors that use atomic save (write to temp, then rename).
+	configDir := filepath.Dir(w.configPath)
+	if errAddConfig := w.watcher.Add(configDir); errAddConfig != nil {
+		log.Errorf("failed to watch config directory %s: %v", configDir, errAddConfig)
 		return errAddConfig
 	}
-	log.Debugf("watching config file: %s", w.configPath)
+	log.Debugf("watching config directory: %s (for file: %s)", configDir, filepath.Base(w.configPath))
 
 	// Watch the auth directory
 	if errAddAuthDir := w.watcher.Add(w.authDir); errAddAuthDir != nil {
@@ -700,7 +702,23 @@ func (w *Watcher) isKnownAuthFile(path string) bool {
 func (w *Watcher) handleEvent(event fsnotify.Event) {
 	// Filter only relevant events: config file or auth-dir JSON files.
 	configOps := fsnotify.Write | fsnotify.Create | fsnotify.Rename
-	isConfigEvent := event.Name == w.configPath && event.Op&configOps != 0
+	// Check if this event is for our config file (handle both exact match and basename match for directory watching)
+	isConfigEvent := false
+	if event.Op&configOps != 0 {
+		// Exact path match
+		if event.Name == w.configPath {
+			isConfigEvent = true
+		} else {
+			// Check if basename matches and it's in the config directory (for atomic save detection)
+			configDir := filepath.Dir(w.configPath)
+			configBase := filepath.Base(w.configPath)
+			eventDir := filepath.Dir(event.Name)
+			eventBase := filepath.Base(event.Name)
+			if eventDir == configDir && eventBase == configBase {
+				isConfigEvent = true
+			}
+		}
+	}
 	authOps := fsnotify.Create | fsnotify.Write | fsnotify.Remove | fsnotify.Rename
 	isAuthJSON := strings.HasPrefix(event.Name, w.authDir) && strings.HasSuffix(event.Name, ".json") && event.Op&authOps != 0
 	if !isConfigEvent && !isAuthJSON {