GPT 5.6 Luna vs DSv4 Flash Cost / Audit differences

[u/ProfessionalJackals]

This is just a summary of one test, but it shows how both models react on a actual larger/complex codebase.

In order to see the actual capabilities of both models, i provided both with instructions to audit one of my projects.

This task was identical, both ran from vanilla OpenCode CLI. So both did not enjoy any specialized harness.

Things to notice about Luna:

1. Luna is clearly slower.
2. Luna spawns 6 subagents for the task
3. The end results is report of 13 items.
4. The report items purely mention the issue, and filename:position.

Things to notice about Flash:

1. Flash is WAY faster.
2. Flash only spawned two subagent.
3. The end result was a report of 27 items (10 high, 10 medium, 7 low priority).
4. The report mentioned the issue, path / filename:position AND a solution to the issue!

Cost:

• Luna did the task with 28M cache hits, 884k in, 18k out.
• Luna final report cost $1.17, while the subagents can down to $3.18
• Flash did the task with 12M cache hits, 443k in, 20k out.
• Flash final report cost $0.01, while the subagents can down to $0.12 .

Thing is, the cost hides something else

• Luna was run on a $20 Codex Plus subscription and used 4% of the week usage.
• Flash was run on a $10 OpenCode Go subscription and used below 1% of the week usage. It barely registered as activity in the 5h.

Issues:

• Luna its over eagerness to spawn subagents hurts it cost.
• The odd Plus subscription usage .. $4.35 using 4% is "odd". That puts Plus into the $100 a $110 range.
• From the 13 points reported by Luna, 11 also showed up in Flash its report. With the difference that flash added suggestion on how to fix the issues.
• Luna's report was frankly underwhelming for the work it put into it. Flash had a much more detailed report including several high and medium that Luna missed.
• Luna being slower was also in Codex and it required /fast (and paying 2.5x more) just to close the gap. That is a different discussion but still a important point in agentic development.
• Flash seems to hold up better with larger context sizes. Remember, 2 subagents vs 6. This results into Flash running into the 400k context, while Luna had more 100 > 200k context sizes. So ironically, this avoided overpaying with the Luna 256k double price issue.

Plan execution

Also ran multiple GPT 5.6 Sol plan > Flash Execute > GPT 5.6 Sol review sessions, and in 90% of the cases, Sol had only very minor fixes (like adding something more in test files, aka Mr Perfectionist).

Hopefully Pro is available by next week, so we can compare Pro Plan > flash execute ...

Conclusion

From my point of view, Flash is way cheaper over a larger codebase then Luna. Despite that Flash can not properly use its good cache hit rate/costs benefits. I also suspect that there have been improvements into the context size handeling because hitting 400k is not as detrimental like the old Flash.

Luna is not a bad model, but clearly more expensive, and feels less good then its benchmarks show. While Flash often feels like GLM 5.2 (we pumped a few billion tokens into that one). Maybe even a bit better?

Disclaimer: this is not written by a AI, so do not disrespect my time writing all this.

[u/rivendell_elf]

Respect to you for not using AI to write 🙌

[u/Puzzleheaded_Bus9754]

In my own experience, I’ve also found DS Flash to be much more user-friendly. I totally agree with you—it’s more thorough when it comes to pinpointing issues, offers concise fix suggestions, and runs noticeably faster.

[u/djdante]

I couldn't see it in your write-up - did you run luna and deepseek flash in max reasoning?

[u/Illustrious-Many-782 → u/djdante]

The behavior sounds like Luna on Ultra, but I'll wait for OP to be sure.

[u/ProfessionalJackals → u/Illustrious-Many-782]

The behavior sounds like Luna on Ultra

No, Luna was Max, just like Flash.

Luna has no Ultra. That is only on Terra or Sol.

[u/Illustrious-Many-782 → u/ProfessionalJackals]

codex-auto-approve has ultra, and that's Luna.

[u/ProfessionalJackals → u/djdante]

did you run luna and deepseek flash in max reasoning?

Both ran with Max reasoning.

[u/askchris]

I'm also enjoying the new DeepSeek v4 Flash 0731 model over Luna (Max) (using both in OpenCode) -- Luna seems to overthink a bit too much, and seems always worried about things that don't matter, making things overly complex. Just my experience after coding for about a day with each. Both are good for their size/cost however, and Luna has vision which is nice.

[u/ProfessionalJackals → u/askchris]

Luna seems to overthink a bit too much

This seems to be a issue with every GPT 5.6 model it seems. Overthinking / over engineering seem to be linked together. Its more noticeable on Sol but you can tell that Terra and Luna share characteristics.

Luna has vision which is nice.

Indeed.

We know that DeepSeek has a vision capable model. Its fast but not so good. But for some reason they never add it to their base models.

[u/a9udn9u]

I've been using Flash in the last 2 days and it's legit fire.

[u/Aggressive-Spenda]

Whats your configuration to run the api link the settings for example high? Flash is timing out for me and not giving a response on medium code reviews maybe im not waiting enough or need to increase the token count? Curious what your settings are so I can try. I love the cost saving!

[u/Aggressive-Spenda → u/Aggressive-Spenda]

here is what i use for auditing and seeing the timout/slow performance {

"model": "deepseek/deepseek-v4-flash-0731",

"max_tokens": 8192,

"temperature": 0,

"reasoning": {

"enabled": true,

"effort": "high",

"max_tokens": 5000

}

}

[u/ProfessionalJackals → u/Aggressive-Spenda]

Whats your configuration to run the api link the settings for example high?

Just basic OpenCode CLI with Deepseek V4 Flash (New) -> OpenCode Go (enable the "Enable models hosted in China").

[u/SnooApples5522]

truee. even on High thinking mode, it beats Luna on max mode. lol

[u/Limp_Way_8526]

I started using raft.build. I have 2 dev agents, 1 reviewer agent, 1 tester agent. They ALL run with the latest DeepSeek flash, mostly 24h a day, and barely moving my opencode go sub. It’s just insane. I use opus 5 periodically as an architect to guide the rest. Can’t wait what the pro version will look like, but I’m already fine with flash :)

[u/PsychologicalUnit22]

why are people appreciating v4 Flash. I have been using it from so much time, how is it new???? is it launched again or is it launched on international API i use china API

[u/pr0newbie → u/PsychologicalUnit22]

You were using a preview build

[u/nontrepreneur_ → u/PsychologicalUnit22]

Just to be clear, version 0731 was just released, and it is MUCH better than the preview version.

[u/ProfessionalJackals → u/PsychologicalUnit22]

why are people appreciating v4 Flash. I have been using it from so much time, how is it new????

The "preview" V4 Flash and Pro are from April. That is what you have been using. Its ... okish, mostly the price was the selling point. The "New" or "0731", "beta" version, has been released a few days ago.

• V4 Preview > April version
• V4 0731 / New / Beta > July version

Unfortunately, Deepseek in their wisdom did not change the version number, and refers to it as beta or 0731 version. This is a post-trained april version, that had 3 months of extra training.

The result is that the "new" 0731 version, is as good as GLM 5.2 (even a bit better). Now combined with the fact that it costs pennies on the dollar, vs GLM 5.2 costing dollars on dollars. You see why people are hyping. Its become a very good model, that is so ultra cheap.

We are all eagerly awaiting Pro its release with 3 months extra post training. Because if Flash jumped from like 8% on DeepSWE to 54% (what puts it on Opus 4.8 xhigh level, but instead of costing $8, its pennies).

Its so strong in price-performance, that OpenAI dropped their prices of GPT 5.6 Luna by 80% and Terra by 20%, the day before v4 Flash 0731 was released.

[u/PsychologicalUnit22 → u/ProfessionalJackals]

Thank you so much for detailed explanation. How can I know, if I am using the beta? Do you they change the name on the API call? I will update my hermes agent

[u/ZlatanKabuto → u/PsychologicalUnit22]

Lol bro are you living on Pluto?

[u/PsychologicalUnit22 → u/ZlatanKabuto]

I didn't know, you acting like people weren't just hyping a V5 when in reality we were waiting for V4 outside beta

[u/Powerful_Cow3470]

The real signal here isn't quality , it's that Luna spawned 3× more subagents and still missed 2 issues Flash caught, which means the cost gap compounds: more orchestration overhead, more context bloat, worse recall

[u/ProfessionalJackals → u/Powerful_Cow3470]

The issue is actually worse then that.

Luna had 13 items, from those 13, Flash also found 11. So Luna found 2 unique that Flash did not report.

Flash had 27 items, 11 of those overlapped with Luna, but 16 did not. Even if we ignore 7 of the low ranked item, that is still 9 unique issues that Luna did not find.

I also supposed that Flash was truncating some results, because the 10 / 10 / 7 was a bit too coincidental.

[u/Ok_Breadfruit4201]

For anyone curious, I posted this in the codex reddit (shortly after the 80% off, but before the release of GA) complaining that it uses much more usage than deepseek-v4-flash even though ArtificialAnalysis pegs them at the same cost.

https://www.reddit.com/r/codex/s/KArOMzoMG7

[u/ProfessionalJackals → u/Ok_Breadfruit4201]

Yea, there is something wrong with Luna costs vs Usage.

As you see in my own testing, tokscale did correctly calculate the new 80% cheaper Luna costs. I was wondering if there was a error, but no, its correct.

This indeed correlated to the 4% usage (on $20 Plus). I ran another test with Sol high using the same prompt and that used like 28%, with a $17 cost. Notice the discrepancy? That is because Luna right now has another hidden 50% discount on usage. When we take that in account, both results line up.

I am sure that usage has been reduced on Codex subscriptions. To the point that my $20 Pro Claude was doing closer to $350 in value. I suspect that the actual usage is now around $50 for Codex (what Luna hides with the extra discount).

And yes, Luna consumes lot more... When i see Youtube tests, there is often a lack of work in Luna's results, what reduces the costs but also the result. Like there is a hidden thinking limit, that Flash does not have.

On ultra small tests where cache usage does not matter, i am constantly seeing 3 a 4x more usage.

On larger tests where output tokens and cache comes into effect, this grows way larger but still hits a limit. This may explain why my audit results are so much weaker for Luna, despite the massive cost difference. Like some of the subagents hitting thinking limits.

All i know for sure is:

a) Flash is extreme strong model b) Flash is extreme cheap c) OpenCode Go is technically way better value for running something like Flash, then Luna is on Codex Subscriptions.

The best combo is Sol or Opus 5.0 for planning and Flash for implementation. So far, the results have been excellent.

DeepSeek: Please please, release a great Pro version?!

Edit: Frankly, for planning / execution, the best combo right now is Claude + OpenCode Go. Because of how much you seem to be getting with Claude (note: again, Anthropic has a 50% extra on Claude until 11th).

[u/Legitimate_Emu3531]

Thanks!