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: 6.0s, slowest single call: 2.2s. Running them concurrently saves 3.8s — a 2.7× speedup.

Now (sequential)After fix (parallel)

6.0s

→

~2.2s

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 › planerror

agent.plan

user: u_heavy_14

6.08s

anthropic › messages › create

anthropic.messages.create

claude-opus-4-7910 tok$0.035faithful 0.59user: u_heavy_14

1.90s

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-4-72.9k tok$0.114faithful 0.55user: u_heavy_14

1.85s

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 › createerror

anthropic.messages.create

claude-opus-4-72.8k tok$0.110faithful 0.54user: u_heavy_14

2.23s

Input

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

Output

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

Faithfulness · anthropic.messages.create0.50

2 supported · 1 contradicted · 1 unsupported of 4 claims

supported
Policy P-204(b) applies to this request.
contradicted
The refund amount is $189.99.
unsupported
The card on file ends in 4421.
supported
Refunds settle within 3 business days.

Faithfulness · anthropic.messages.create0.50

2 supported · 1 contradicted · 1 unsupported of 4 claims

supported
Policy P-204(b) applies to this request.
contradicted
The refund amount is $189.99.
unsupported
The card on file ends in 4421.
supported
Refunds settle within 3 business days.