From 4964e02465f2e9b4f98fbbf49f2fe058892b715d Mon Sep 17 00:00:00 2001
From: Dmitry Vyukov <dvyukov@google.com>
Date: Mon, 26 Jan 2026 15:07:39 +0100
Subject: pkg/aflow/trajectory: add token usage

---
 pkg/aflow/llm_agent.go             | 16 +++++++++++-----
 pkg/aflow/trajectory/trajectory.go |  8 ++++++++
 2 files changed, 19 insertions(+), 5 deletions(-)

(limited to 'pkg')

diff --git a/pkg/aflow/llm_agent.go b/pkg/aflow/llm_agent.go
index 6cb84b5a3..2c83be2eb 100644
--- a/pkg/aflow/llm_agent.go
+++ b/pkg/aflow/llm_agent.go
@@ -192,8 +192,7 @@ func (a *LLMAgent) chat(ctx *Context, cfg *genai.GenerateContentConfig, tools ma
 		if err != nil {
 			return "", nil, ctx.finishSpan(reqSpan, err)
 		}
-		reply, thoughts, calls, respErr := a.parseResponse(resp)
-		reqSpan.Thoughts = thoughts
+		reply, calls, respErr := a.parseResponse(resp, reqSpan)
 		if err := ctx.finishSpan(reqSpan, respErr); err != nil {
 			return "", nil, err
 		}
@@ -302,8 +301,8 @@ func (a *LLMAgent) callTools(ctx *Context, tools map[string]Tool, calls []*genai
 	return responses, outputs, nil
 }
 
-func (a *LLMAgent) parseResponse(resp *genai.GenerateContentResponse) (
-	reply, thoughts string, calls []*genai.FunctionCall, err error) {
+func (a *LLMAgent) parseResponse(resp *genai.GenerateContentResponse, span *trajectory.Span) (
+	reply string, calls []*genai.FunctionCall, err error) {
 	if len(resp.Candidates) == 0 || resp.Candidates[0] == nil {
 		err = fmt.Errorf("empty model response")
 		if resp.PromptFeedback != nil {
@@ -322,6 +321,13 @@ func (a *LLMAgent) parseResponse(resp *genai.GenerateContentResponse) (
 		err = fmt.Errorf("unexpected reply fields (%+v)", *candidate)
 		return
 	}
+	if resp.UsageMetadata != nil {
+		// We add ToolUsePromptTokenCount just in case, but Gemini does not use/set it.
+		span.InputTokens = int(resp.UsageMetadata.PromptTokenCount) +
+			int(resp.UsageMetadata.ToolUsePromptTokenCount)
+		span.OutputTokens = int(resp.UsageMetadata.CandidatesTokenCount)
+		span.OutputThoughtsTokens = int(resp.UsageMetadata.ThoughtsTokenCount)
+	}
 	for _, part := range candidate.Content.Parts {
 		// We don't expect to receive these now.
 		if part.VideoMetadata != nil || part.InlineData != nil ||
@@ -333,7 +339,7 @@ func (a *LLMAgent) parseResponse(resp *genai.GenerateContentResponse) (
 		if part.FunctionCall != nil {
 			calls = append(calls, part.FunctionCall)
 		} else if part.Thought {
-			thoughts += part.Text
+			span.Thoughts += part.Text
 		} else {
 			reply += part.Text
 		}
diff --git a/pkg/aflow/trajectory/trajectory.go b/pkg/aflow/trajectory/trajectory.go
index ad22b018e..fc63235cf 100644
--- a/pkg/aflow/trajectory/trajectory.go
+++ b/pkg/aflow/trajectory/trajectory.go
@@ -38,6 +38,12 @@ type Span struct {
 
 	// LLM invocation.
 	Thoughts string `json:",omitzero"`
+
+	// For details see:
+	// https://pkg.go.dev/google.golang.org/genai#GenerateContentResponseUsageMetadata
+	InputTokens          int `json:",omitzero"`
+	OutputTokens         int `json:",omitzero"`
+	OutputThoughtsTokens int `json:",omitzero"`
 }
 
 type SpanType string
@@ -89,6 +95,8 @@ func (span *Span) String() string {
 			}
 			fmt.Fprintf(sb, "reply:\n%v\n", span.Reply)
 		case SpanLLM:
+			fmt.Fprintf(sb, "tokens: input=%v output=%v thoughts=%v\n",
+				span.InputTokens, span.OutputTokens, span.OutputThoughtsTokens)
 			if span.Thoughts != "" {
 				fmt.Fprintf(sb, "thoughts:\n%v\n", span.Thoughts)
 			}
-- 
cgit mrf-deployment