@@ -633,7 +633,11 @@ func (c *coordinator) buildProvider(providerCfg config.ProviderConfig, model con
633633
634634 // handle special headers for anthropic
635635 if providerCfg.Type == anthropic.Name && c.isAnthropicThinking(model) {
636− headers["anthropic-beta"] = "interleaved-thinking-2025-05-14"
636+ if v, ok := headers["anthropic-beta"]; ok {
637+ headers["anthropic-beta"] = v + ",interleaved-thinking-2025-05-14"
638+ } else {
639+ headers["anthropic-beta"] = "interleaved-thinking-2025-05-14"
640+ }
637641 }
638642
639643 // TODO: make sure we have