diff --git a/agent.go b/agent.go
index 6f628b0a7a593681d8001f9f0f0637ac736f807b..87542032219840a6a025ffb5538de75d4758d90c 100644
--- a/agent.go
+++ b/agent.go
@@ -841,7 +841,7 @@ func (a *agent) Stream(ctx context.Context, opts AgentStreamCall) (*AgentResult,
 }
 
 func (a *agent) prepareTools(tools []AgentTool, activeTools []string, disableAllTools bool) []Tool {
-	var preparedTools []Tool
+	preparedTools := make([]Tool, 0, len(tools))
 
 	// If explicitly disabling all tools, return no tools
 	if disableAllTools {
diff --git a/content.go b/content.go
index 375f216972b1b46c951c54d6b3fa1e9454b07829..5ff7f0805aa7a6a533527e4525cfb657dff9750a 100644
--- a/content.go
+++ b/content.go
@@ -469,7 +469,7 @@ func NewUserMessage(prompt string, files ...FilePart) Message {
 }
 
 func NewSystemMessage(prompt ...string) Message {
-	var content []MessagePart
+	content := make([]MessagePart, 0, len(prompt))
 	for _, p := range prompt {
 		content = append(content, TextPart{Text: p})
 	}
diff --git a/providers/openai.go b/providers/openai.go
index 3e1832c4944b4109373d1874336c6f6a4c48e9c3..c9d396e4343cac1fcf263aee22231d7de91f56ae 100644
--- a/providers/openai.go
+++ b/providers/openai.go
@@ -436,7 +436,7 @@ func (o openAiLanguageModel) Generate(ctx context.Context, call ai.Call) (*ai.Re
 		return nil, errors.New("no response generated")
 	}
 	choice := response.Choices[0]
-	var content []ai.Content
+	content := make([]ai.Content, 0, 1+len(choice.Message.ToolCalls)+len(choice.Message.Annotations))
 	text := choice.Message.Content
 	if text != "" {
 		content = append(content, ai.TextContent{