Root cause: sequential execution of "messages.create"

3 "anthropic.messages.create" spans ran one after another — each started only after the previous one finished. Total: 5.7s, slowest single call: 2.3s. Running them concurrently saves 3.4s — a 2.5× speedup.

Now (sequential)After fix (parallel)

5.7s

→

~2.3s

Fix: run calls in parallel

fix.py

from concurrent.futures import ThreadPoolExecutor

# Before — sequential, each call blocks the next:
for item in items:
    result = process(item)

# After — all calls run concurrently:
with ThreadPoolExecutor(max_workers=8) as pool:
    results = list(pool.map(process, items))

# Cost unchanged. Output unchanged. Time = slowest single call.

Waterfall

agent › plan

agent.plan

user: u_775

6.74s

anthropic › messages › create

anthropic.messages.create

claude-opus-4-73.0k tok$0.117faithful 0.63user: u_775

1.20s

Input

Summarize the Q3 earnings report attached. Focus on revenue, margin, and guidance.

Output

(answer to: Summarize the Q3 earnings report attache…)

anthropic › messages › create

anthropic.messages.create

claude-opus-4-72.3k tok$0.090faithful 0.97user: u_775

2.19s

Input

Given the customer ticket below, draft a refund response that follows policy P-204.

Output

(answer to: Given the customer ticket below, draft a…)

anthropic › messages › create

anthropic.messages.create

claude-opus-4-72.2k tok$0.085faithful 0.90user: u_775

2.26s

Input

Translate the user manual section to Japanese, preserving the table structure.

Output

(answer to: Translate the user manual section to Jap…)

Tool: calculator

tool.calculator

user: u_775

480ms

Tool: code_exec

tool.code_exec

user: u_775

521ms

Faithfulness · anthropic.messages.create0.50

1 supported · 0 contradicted · 1 unsupported of 2 claims

unsupported
All chapters were translated.
supported
Tables were preserved in the output.