GPT-5.6 Luna (August) on HealthBench Professional

rank 19 of 22 · updated September 8, 2026

GPT-5.6 Luna (August) scores 0.441 on HealthBench Professional, rank 19 of 22 models on the board. The small, high-volume tier of the GPT-5.6 family, repriced to $0.20 per million input tokens on July 30, 2026. HealthBench Professional scores models on 525 tasks drawn from real clinician conversations, graded criterion by criterion against physician-written rubrics on a 0 to 1 scale.

Result and API facts

rank	19 of 22
score	0.441
lab	OpenAI
context window	1.1M tokens
API price per 1M tokens	$0.20 in / $1.20 out
license	proprietary
source	GPT-5.6 - August Updates (system card addendum) (system card)
released	2026-07-09

Position in the field

The gap to the leader, Claude Fable 5 at 0.660, is 0.219. Directly above sits Claude Sonnet 4.6 at 0.442. Directly below sits GPT-5.1 at 0.396. The scores on this page are compiled from published documents rather than from one controlled run, so a small gap between 2 models can reflect a difference in grader version, reasoning effort, or deployment setting as well as a difference in capability.

Source of this score

Read from GPT-5.6 - August Updates (system card addendum) (system card, OpenAI, 2026-08-06). Vendor-reported. Confidence: verified. Configuration: ChatGPT production (Instant) deployment setting, length-adjusted, GPT-5.6 August Updates PDF column GPT-5.6 Luna (August) (46.8 unadjusted, 2,920 chars).

HealthBench Professional 32.9 (33.8, 2,285) 38.4 (40.7, 2,775) 54.0 (56.6, 2,894) 44.1 (46.8, 2,920)

p. 11, section 5.1 HealthBench, table "Reported as length-adjusted score (unadjusted, mean response length in characters)", column GPT-5.6 Luna (August) · full entry on the sources page

What does GPT-5.6 Luna (August) score on HealthBench Professional?

GPT-5.6 Luna (August) scores 0.441 on HealthBench Professional, which places it at rank 19 of 22 models on the board as of September 8, 2026. The number was read from GPT-5.6 - August Updates (system card addendum), listed on the sources page.

How much does GPT-5.6 Luna (August) cost to run?

GPT-5.6 Luna (August) is priced at $0.20 per million input tokens and $1.20 per million output tokens through OpenAI's API.

Head to head

Pairings with a dedicated comparison page are linked; every other difference is in the score-difference matrix.

GPT-5.6 Luna (August) vs Claude Fable 5
0.441 vs 0.660 · Claude Fable 5 by 0.219
GPT-5.6 Luna (August) vs GPT-6 Astra
0.441 vs 0.634 · GPT-6 Astra by 0.193
GPT-5.6 Luna (August) vs Claude Fable 5.1
0.441 vs 0.621 · Claude Fable 5.1 by 0.180
GPT-5.6 Luna (August) vs GPT-5.6 Sol
0.441 vs 0.605 · GPT-5.6 Sol by 0.164
GPT-5.6 Luna (August) vs Claude Opus 5
0.441 vs 0.598 · Claude Opus 5 by 0.157
GPT-5.6 Luna (August) vs Muse Spark 1.1
0.441 vs 0.593 · Muse Spark 1.1 by 0.152
GPT-5.6 Luna (August) vs Claude Sonnet 5
0.441 vs 0.578 · Claude Sonnet 5 by 0.137
GPT-5.6 Luna (August) vs GPT-5.6 Terra
0.441 vs 0.577 · GPT-5.6 Terra by 0.136
GPT-5.6 Luna (August) vs Claude Opus 4.8
0.441 vs 0.558 · Claude Opus 4.8 by 0.117
GPT-5.6 Luna (August) vs GPT-5.6 Luna
0.441 vs 0.557 · GPT-5.6 Luna by 0.116
GPT-5.6 Luna (August) vs Muse Spark
0.441 vs 0.541 · Muse Spark by 0.100
GPT-5.6 Luna (August) vs GPT-5.6 Sol (August)
0.441 vs 0.540 · GPT-5.6 Sol (August) by 0.099
GPT-5.6 Luna (August) vs Claude Opus 4.7
0.441 vs 0.519 · Claude Opus 4.7 by 0.078
GPT-5.6 Luna (August) vs GPT-5.5
0.441 vs 0.518 · GPT-5.5 by 0.077
GPT-5.6 Luna (August) vs GPT-5.4
0.441 vs 0.481 · GPT-5.4 by 0.040
GPT-5.6 Luna (August) vs GPT-5
0.441 vs 0.462 · GPT-5 by 0.021
GPT-5.6 Luna (August) vs GPT-5.2
0.441 vs 0.459 · GPT-5.2 by 0.018
GPT-5.6 Luna (August) vs Claude Sonnet 4.6
0.441 vs 0.442 · Claude Sonnet 4.6 by 0.001
GPT-5.6 Luna (August) vs GPT-5.1
0.441 vs 0.396 · GPT-5.6 Luna (August) by 0.045
GPT-5.6 Luna (August) vs GPT-5.5 Instant
0.441 vs 0.384 · GPT-5.6 Luna (August) by 0.057
GPT-5.6 Luna (August) vs MAI-Thinking-1
0.441 vs 0.350 · GPT-5.6 Luna (August) by 0.091

Where the scores come from and how they are read is on the methodology page. The full ranking is on the leaderboard.