diff --git a/internal/config/config.go b/internal/config/config.go
index d6e2bdc8..5a6595f7 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -516,16 +516,6 @@ func LoadConfig(configFile string) (*Config, error) {
 // If optional is true and the file is missing, it returns an empty Config.
 // If optional is true and the file is empty or invalid, it returns an empty Config.
 func LoadConfigOptional(configFile string, optional bool) (*Config, error) {
-	// NOTE: Startup oauth-model-alias migration is intentionally disabled.
-	// Reason: avoid mutating config.yaml during server startup.
-	// Re-enable the block below if automatic startup migration is needed again.
-	// if migrated, err := MigrateOAuthModelAlias(configFile); err != nil {
-	// 	// Log warning but don't fail - config loading should still work
-	// 	fmt.Printf("Warning: oauth-model-alias migration failed: %v\n", err)
-	// } else if migrated {
-	// 	fmt.Println("Migrated oauth-model-mappings to oauth-model-alias")
-	// }
-
 	// Read the entire configuration file into memory.
 	data, err := os.ReadFile(configFile)
 	if err != nil {
@@ -1560,9 +1550,6 @@ func pruneMappingToGeneratedKeys(dstRoot, srcRoot *yaml.Node, key string) {
 	srcIdx := findMapKeyIndex(srcRoot, key)
 	if srcIdx < 0 {
 		// Keep an explicit empty mapping for oauth-model-alias when it was previously present.
-		//
-		// Rationale: LoadConfig runs MigrateOAuthModelAlias before unmarshalling. If the
-		// oauth-model-alias key is missing, migration will add the default antigravity aliases.
 		// When users delete the last channel from oauth-model-alias via the management API,
 		// we want that deletion to persist across hot reloads and restarts.
 		if key == "oauth-model-alias" {
diff --git a/internal/config/oauth_model_alias_migration.go b/internal/config/oauth_model_alias_migration.go
deleted file mode 100644
index 71613d03..00000000
--- a/internal/config/oauth_model_alias_migration.go
+++ /dev/null
@@ -1,286 +0,0 @@
-package config
-
-import (
-	"os"
-	"strings"
-
-	"gopkg.in/yaml.v3"
-)
-
-// antigravityModelConversionTable maps old built-in aliases to actual model names
-// for the antigravity channel during migration.
-var antigravityModelConversionTable = map[string]string{
-	"gemini-2.5-computer-use-preview-10-2025": "rev19-uic3-1p",
-	"gemini-3-pro-image-preview":              "gemini-3-pro-image",
-	"gemini-3-pro-preview":                    "gemini-3-pro-high",
-	"gemini-3-flash-preview":                  "gemini-3-flash",
-	"gemini-3.1-pro-preview":                  "gemini-3.1-pro-high",
-	"gemini-claude-sonnet-4-5":                "claude-sonnet-4-6",
-	"gemini-claude-sonnet-4-5-thinking":       "claude-sonnet-4-6-thinking",
-	"gemini-claude-opus-4-5-thinking":         "claude-opus-4-6-thinking",
-	"gemini-claude-opus-4-6-thinking":         "claude-opus-4-6-thinking",
-	"gemini-claude-sonnet-4-6":                "claude-sonnet-4-6",
-	"claude-sonnet-4-5":                       "claude-sonnet-4-6",
-	"claude-sonnet-4-5-thinking":              "claude-sonnet-4-6-thinking",
-	"claude-opus-4-5-thinking":                "claude-opus-4-6-thinking",
-}
-
-// defaultAntigravityAliases returns the default oauth-model-alias configuration
-// for the antigravity channel when neither field exists.
-func defaultAntigravityAliases() []OAuthModelAlias {
-	return []OAuthModelAlias{
-		{Name: "rev19-uic3-1p", Alias: "gemini-2.5-computer-use-preview-10-2025"},
-		{Name: "gemini-3-pro-image", Alias: "gemini-3-pro-image-preview"},
-		{Name: "gemini-3-pro-high", Alias: "gemini-3-pro-preview"},
-		{Name: "gemini-3-flash", Alias: "gemini-3-flash-preview"},
-		{Name: "gemini-3.1-pro-high", Alias: "gemini-3.1-pro-preview"},
-		{Name: "claude-sonnet-4-6", Alias: "gemini-claude-sonnet-4-5"},
-		{Name: "claude-sonnet-4-6-thinking", Alias: "gemini-claude-sonnet-4-5-thinking"},
-		{Name: "claude-sonnet-4-6", Alias: "claude-sonnet-4-5"},
-		{Name: "claude-sonnet-4-6-thinking", Alias: "claude-sonnet-4-5-thinking"},
-		{Name: "claude-opus-4-6-thinking", Alias: "gemini-claude-opus-4-5-thinking"},
-		{Name: "claude-opus-4-6-thinking", Alias: "claude-opus-4-5-thinking"},
-		{Name: "claude-opus-4-6-thinking", Alias: "gemini-claude-opus-4-6-thinking"},
-	}
-}
-
-// MigrateOAuthModelAlias checks for and performs migration from oauth-model-mappings
-// to oauth-model-alias at startup. Returns true if migration was performed.
-//
-// Migration flow:
-// 1. Check if oauth-model-alias exists -> skip migration
-// 2. Check if oauth-model-mappings exists -> convert and migrate
-//   - For antigravity channel, convert old built-in aliases to actual model names
-//
-// 3. Neither exists -> add default antigravity config
-func MigrateOAuthModelAlias(configFile string) (bool, error) {
-	data, err := os.ReadFile(configFile)
-	if err != nil {
-		if os.IsNotExist(err) {
-			return false, nil
-		}
-		return false, err
-	}
-	if len(data) == 0 {
-		return false, nil
-	}
-
-	// Parse YAML into node tree to preserve structure
-	var root yaml.Node
-	if err := yaml.Unmarshal(data, &root); err != nil {
-		return false, nil
-	}
-	if root.Kind != yaml.DocumentNode || len(root.Content) == 0 {
-		return false, nil
-	}
-	rootMap := root.Content[0]
-	if rootMap == nil || rootMap.Kind != yaml.MappingNode {
-		return false, nil
-	}
-
-	// Check if oauth-model-alias already exists
-	if findMapKeyIndex(rootMap, "oauth-model-alias") >= 0 {
-		return false, nil
-	}
-
-	// Check if oauth-model-mappings exists
-	oldIdx := findMapKeyIndex(rootMap, "oauth-model-mappings")
-	if oldIdx >= 0 {
-		// Migrate from old field
-		return migrateFromOldField(configFile, &root, rootMap, oldIdx)
-	}
-
-	// Neither field exists - add default antigravity config
-	return addDefaultAntigravityConfig(configFile, &root, rootMap)
-}
-
-// migrateFromOldField converts oauth-model-mappings to oauth-model-alias
-func migrateFromOldField(configFile string, root *yaml.Node, rootMap *yaml.Node, oldIdx int) (bool, error) {
-	if oldIdx+1 >= len(rootMap.Content) {
-		return false, nil
-	}
-	oldValue := rootMap.Content[oldIdx+1]
-	if oldValue == nil || oldValue.Kind != yaml.MappingNode {
-		return false, nil
-	}
-
-	// Parse the old aliases
-	oldAliases := parseOldAliasNode(oldValue)
-	if len(oldAliases) == 0 {
-		// Remove the old field and write
-		removeMapKeyByIndex(rootMap, oldIdx)
-		return writeYAMLNode(configFile, root)
-	}
-
-	// Convert model names for antigravity channel
-	newAliases := make(map[string][]OAuthModelAlias, len(oldAliases))
-	for channel, entries := range oldAliases {
-		converted := make([]OAuthModelAlias, 0, len(entries))
-		for _, entry := range entries {
-			newEntry := OAuthModelAlias{
-				Name:  entry.Name,
-				Alias: entry.Alias,
-				Fork:  entry.Fork,
-			}
-			// Convert model names for antigravity channel
-			if strings.EqualFold(channel, "antigravity") {
-				if actual, ok := antigravityModelConversionTable[entry.Name]; ok {
-					newEntry.Name = actual
-				}
-			}
-			converted = append(converted, newEntry)
-		}
-		newAliases[channel] = converted
-	}
-
-	// For antigravity channel, supplement missing default aliases
-	if antigravityEntries, exists := newAliases["antigravity"]; exists {
-		// Build a set of already configured model names (upstream names)
-		configuredModels := make(map[string]bool, len(antigravityEntries))
-		for _, entry := range antigravityEntries {
-			configuredModels[entry.Name] = true
-		}
-
-		// Add missing default aliases
-		for _, defaultAlias := range defaultAntigravityAliases() {
-			if !configuredModels[defaultAlias.Name] {
-				antigravityEntries = append(antigravityEntries, defaultAlias)
-			}
-		}
-		newAliases["antigravity"] = antigravityEntries
-	}
-
-	// Build new node
-	newNode := buildOAuthModelAliasNode(newAliases)
-
-	// Replace old key with new key and value
-	rootMap.Content[oldIdx].Value = "oauth-model-alias"
-	rootMap.Content[oldIdx+1] = newNode
-
-	return writeYAMLNode(configFile, root)
-}
-
-// addDefaultAntigravityConfig adds the default antigravity configuration
-func addDefaultAntigravityConfig(configFile string, root *yaml.Node, rootMap *yaml.Node) (bool, error) {
-	defaults := map[string][]OAuthModelAlias{
-		"antigravity": defaultAntigravityAliases(),
-	}
-	newNode := buildOAuthModelAliasNode(defaults)
-
-	// Add new key-value pair
-	keyNode := &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: "oauth-model-alias"}
-	rootMap.Content = append(rootMap.Content, keyNode, newNode)
-
-	return writeYAMLNode(configFile, root)
-}
-
-// parseOldAliasNode parses the old oauth-model-mappings node structure
-func parseOldAliasNode(node *yaml.Node) map[string][]OAuthModelAlias {
-	if node == nil || node.Kind != yaml.MappingNode {
-		return nil
-	}
-	result := make(map[string][]OAuthModelAlias)
-	for i := 0; i+1 < len(node.Content); i += 2 {
-		channelNode := node.Content[i]
-		entriesNode := node.Content[i+1]
-		if channelNode == nil || entriesNode == nil {
-			continue
-		}
-		channel := strings.ToLower(strings.TrimSpace(channelNode.Value))
-		if channel == "" || entriesNode.Kind != yaml.SequenceNode {
-			continue
-		}
-		entries := make([]OAuthModelAlias, 0, len(entriesNode.Content))
-		for _, entryNode := range entriesNode.Content {
-			if entryNode == nil || entryNode.Kind != yaml.MappingNode {
-				continue
-			}
-			entry := parseAliasEntry(entryNode)
-			if entry.Name != "" && entry.Alias != "" {
-				entries = append(entries, entry)
-			}
-		}
-		if len(entries) > 0 {
-			result[channel] = entries
-		}
-	}
-	return result
-}
-
-// parseAliasEntry parses a single alias entry node
-func parseAliasEntry(node *yaml.Node) OAuthModelAlias {
-	var entry OAuthModelAlias
-	for i := 0; i+1 < len(node.Content); i += 2 {
-		keyNode := node.Content[i]
-		valNode := node.Content[i+1]
-		if keyNode == nil || valNode == nil {
-			continue
-		}
-		switch strings.ToLower(strings.TrimSpace(keyNode.Value)) {
-		case "name":
-			entry.Name = strings.TrimSpace(valNode.Value)
-		case "alias":
-			entry.Alias = strings.TrimSpace(valNode.Value)
-		case "fork":
-			entry.Fork = strings.ToLower(strings.TrimSpace(valNode.Value)) == "true"
-		}
-	}
-	return entry
-}
-
-// buildOAuthModelAliasNode creates a YAML node for oauth-model-alias
-func buildOAuthModelAliasNode(aliases map[string][]OAuthModelAlias) *yaml.Node {
-	node := &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}
-	for channel, entries := range aliases {
-		channelNode := &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: channel}
-		entriesNode := &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq"}
-		for _, entry := range entries {
-			entryNode := &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}
-			entryNode.Content = append(entryNode.Content,
-				&yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: "name"},
-				&yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: entry.Name},
-				&yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: "alias"},
-				&yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: entry.Alias},
-			)
-			if entry.Fork {
-				entryNode.Content = append(entryNode.Content,
-					&yaml.Node{Kind: yaml.ScalarNode, Tag: "!!str", Value: "fork"},
-					&yaml.Node{Kind: yaml.ScalarNode, Tag: "!!bool", Value: "true"},
-				)
-			}
-			entriesNode.Content = append(entriesNode.Content, entryNode)
-		}
-		node.Content = append(node.Content, channelNode, entriesNode)
-	}
-	return node
-}
-
-// removeMapKeyByIndex removes a key-value pair from a mapping node by index
-func removeMapKeyByIndex(mapNode *yaml.Node, keyIdx int) {
-	if mapNode == nil || mapNode.Kind != yaml.MappingNode {
-		return
-	}
-	if keyIdx < 0 || keyIdx+1 >= len(mapNode.Content) {
-		return
-	}
-	mapNode.Content = append(mapNode.Content[:keyIdx], mapNode.Content[keyIdx+2:]...)
-}
-
-// writeYAMLNode writes the YAML node tree back to file
-func writeYAMLNode(configFile string, root *yaml.Node) (bool, error) {
-	f, err := os.Create(configFile)
-	if err != nil {
-		return false, err
-	}
-	defer f.Close()
-
-	enc := yaml.NewEncoder(f)
-	enc.SetIndent(2)
-	if err := enc.Encode(root); err != nil {
-		return false, err
-	}
-	if err := enc.Close(); err != nil {
-		return false, err
-	}
-	return true, nil
-}
diff --git a/internal/config/oauth_model_alias_migration_test.go b/internal/config/oauth_model_alias_migration_test.go
deleted file mode 100644
index cd73b9d5..00000000
--- a/internal/config/oauth_model_alias_migration_test.go
+++ /dev/null
@@ -1,245 +0,0 @@
-package config
-
-import (
-	"os"
-	"path/filepath"
-	"strings"
-	"testing"
-
-	"gopkg.in/yaml.v3"
-)
-
-func TestMigrateOAuthModelAlias_SkipsIfNewFieldExists(t *testing.T) {
-	t.Parallel()
-
-	dir := t.TempDir()
-	configFile := filepath.Join(dir, "config.yaml")
-
-	content := `oauth-model-alias:
-  gemini-cli:
-    - name: "gemini-2.5-pro"
-      alias: "g2.5p"
-`
-	if err := os.WriteFile(configFile, []byte(content), 0644); err != nil {
-		t.Fatal(err)
-	}
-
-	migrated, err := MigrateOAuthModelAlias(configFile)
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if migrated {
-		t.Fatal("expected no migration when oauth-model-alias already exists")
-	}
-
-	// Verify file unchanged
-	data, _ := os.ReadFile(configFile)
-	if !strings.Contains(string(data), "oauth-model-alias:") {
-		t.Fatal("file should still contain oauth-model-alias")
-	}
-}
-
-func TestMigrateOAuthModelAlias_MigratesOldField(t *testing.T) {
-	t.Parallel()
-
-	dir := t.TempDir()
-	configFile := filepath.Join(dir, "config.yaml")
-
-	content := `oauth-model-mappings:
-  gemini-cli:
-    - name: "gemini-2.5-pro"
-      alias: "g2.5p"
-      fork: true
-`
-	if err := os.WriteFile(configFile, []byte(content), 0644); err != nil {
-		t.Fatal(err)
-	}
-
-	migrated, err := MigrateOAuthModelAlias(configFile)
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if !migrated {
-		t.Fatal("expected migration to occur")
-	}
-
-	// Verify new field exists and old field removed
-	data, _ := os.ReadFile(configFile)
-	if strings.Contains(string(data), "oauth-model-mappings:") {
-		t.Fatal("old field should be removed")
-	}
-	if !strings.Contains(string(data), "oauth-model-alias:") {
-		t.Fatal("new field should exist")
-	}
-
-	// Parse and verify structure
-	var root yaml.Node
-	if err := yaml.Unmarshal(data, &root); err != nil {
-		t.Fatal(err)
-	}
-}
-
-func TestMigrateOAuthModelAlias_ConvertsAntigravityModels(t *testing.T) {
-	t.Parallel()
-
-	dir := t.TempDir()
-	configFile := filepath.Join(dir, "config.yaml")
-
-	// Use old model names that should be converted
-	content := `oauth-model-mappings:
-  antigravity:
-    - name: "gemini-2.5-computer-use-preview-10-2025"
-      alias: "computer-use"
-    - name: "gemini-3-pro-preview"
-      alias: "g3p"
-`
-	if err := os.WriteFile(configFile, []byte(content), 0644); err != nil {
-		t.Fatal(err)
-	}
-
-	migrated, err := MigrateOAuthModelAlias(configFile)
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if !migrated {
-		t.Fatal("expected migration to occur")
-	}
-
-	// Verify model names were converted
-	data, _ := os.ReadFile(configFile)
-	content = string(data)
-	if !strings.Contains(content, "rev19-uic3-1p") {
-		t.Fatal("expected gemini-2.5-computer-use-preview-10-2025 to be converted to rev19-uic3-1p")
-	}
-	if !strings.Contains(content, "gemini-3-pro-high") {
-		t.Fatal("expected gemini-3-pro-preview to be converted to gemini-3-pro-high")
-	}
-
-	// Verify missing default aliases were supplemented
-	if !strings.Contains(content, "gemini-3-pro-image") {
-		t.Fatal("expected missing default alias gemini-3-pro-image to be added")
-	}
-	if !strings.Contains(content, "gemini-3-flash") {
-		t.Fatal("expected missing default alias gemini-3-flash to be added")
-	}
-	if !strings.Contains(content, "claude-sonnet-4-5") {
-		t.Fatal("expected missing default alias claude-sonnet-4-5 to be added")
-	}
-	if !strings.Contains(content, "claude-sonnet-4-5-thinking") {
-		t.Fatal("expected missing default alias claude-sonnet-4-5-thinking to be added")
-	}
-	if !strings.Contains(content, "claude-opus-4-5-thinking") {
-		t.Fatal("expected missing default alias claude-opus-4-5-thinking to be added")
-	}
-	if !strings.Contains(content, "claude-opus-4-6-thinking") {
-		t.Fatal("expected missing default alias claude-opus-4-6-thinking to be added")
-	}
-}
-
-func TestMigrateOAuthModelAlias_AddsDefaultIfNeitherExists(t *testing.T) {
-	t.Parallel()
-
-	dir := t.TempDir()
-	configFile := filepath.Join(dir, "config.yaml")
-
-	content := `debug: true
-port: 8080
-`
-	if err := os.WriteFile(configFile, []byte(content), 0644); err != nil {
-		t.Fatal(err)
-	}
-
-	migrated, err := MigrateOAuthModelAlias(configFile)
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if !migrated {
-		t.Fatal("expected migration to add default config")
-	}
-
-	// Verify default antigravity config was added
-	data, _ := os.ReadFile(configFile)
-	content = string(data)
-	if !strings.Contains(content, "oauth-model-alias:") {
-		t.Fatal("expected oauth-model-alias to be added")
-	}
-	if !strings.Contains(content, "antigravity:") {
-		t.Fatal("expected antigravity channel to be added")
-	}
-	if !strings.Contains(content, "rev19-uic3-1p") {
-		t.Fatal("expected default antigravity aliases to include rev19-uic3-1p")
-	}
-}
-
-func TestMigrateOAuthModelAlias_PreservesOtherConfig(t *testing.T) {
-	t.Parallel()
-
-	dir := t.TempDir()
-	configFile := filepath.Join(dir, "config.yaml")
-
-	content := `debug: true
-port: 8080
-oauth-model-mappings:
-  gemini-cli:
-    - name: "test"
-      alias: "t"
-api-keys:
-  - "key1"
-  - "key2"
-`
-	if err := os.WriteFile(configFile, []byte(content), 0644); err != nil {
-		t.Fatal(err)
-	}
-
-	migrated, err := MigrateOAuthModelAlias(configFile)
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if !migrated {
-		t.Fatal("expected migration to occur")
-	}
-
-	// Verify other config preserved
-	data, _ := os.ReadFile(configFile)
-	content = string(data)
-	if !strings.Contains(content, "debug: true") {
-		t.Fatal("expected debug field to be preserved")
-	}
-	if !strings.Contains(content, "port: 8080") {
-		t.Fatal("expected port field to be preserved")
-	}
-	if !strings.Contains(content, "api-keys:") {
-		t.Fatal("expected api-keys field to be preserved")
-	}
-}
-
-func TestMigrateOAuthModelAlias_NonexistentFile(t *testing.T) {
-	t.Parallel()
-
-	migrated, err := MigrateOAuthModelAlias("/nonexistent/path/config.yaml")
-	if err != nil {
-		t.Fatalf("unexpected error for nonexistent file: %v", err)
-	}
-	if migrated {
-		t.Fatal("expected no migration for nonexistent file")
-	}
-}
-
-func TestMigrateOAuthModelAlias_EmptyFile(t *testing.T) {
-	t.Parallel()
-
-	dir := t.TempDir()
-	configFile := filepath.Join(dir, "config.yaml")
-
-	if err := os.WriteFile(configFile, []byte(""), 0644); err != nil {
-		t.Fatal(err)
-	}
-
-	migrated, err := MigrateOAuthModelAlias(configFile)
-	if err != nil {
-		t.Fatalf("unexpected error: %v", err)
-	}
-	if migrated {
-		t.Fatal("expected no migration for empty file")
-	}
-}