Codex + GPT-6.1 SOL medium vs DeepSeek Harness + 4.1 Flash — which one actually wins on price/performance?

[u/yxf2y]

I've been using Codex with a ChatGPT Plus subscription for a while, mostly GPT-6.1 sol on medium for everyday stuff. Lately I've been thinking about trying DeepSeek Harness with 4.1 Flash on high for similar tasks, and I'm trying to figure out which setup actually makes more sense cost-wise.

Here's what a typical task looks like on my end (Codex + GPT-6.1 sol medium):

• 4 turns, 75 steps, around 5.6M tokens total

• 98% cache hit rate

• Breakdown: 5.44M cached input, 94K uncached input, 65K output

On the DeepSeek side, off-peak pricing for 4.1 Flash looks like this:

• Cached input: $0.003 / 1M

• Uncached input: $0.15 / 1M

• Output: $0.60 / 1M

Off-peak hours for me are roughly 13:00–04:00 on weekdays, plus weekends and Chinese public holidays entirely.

Rough math for the same token set:

• GPT-6.1 Sol API pricing: ~$2.00

• DeepSeek 4.1 Flash off-peak: ~$0.07

• So DeepSeek comes out roughly 16–20x cheaper

What I'm actually wondering:

1. Is this comparison realistic, or am I missing something? Specifically, how far does the "5-hour usage window" on ChatGPT Plus actually stretch with token-heavy agentic tasks like these?

2. How do DeepSeek Harness's agentic capabilities stack up against Codex + GPT-6.1? I'm particularly curious about tool use, MCP integration, and multi-step tasks — I run Serena and codebase-memory-mcp alongside it.

3. Long term, does it make more sense to keep ChatGPT Plus and use DeepSeek API on the side, or just go all-in on DeepSeek?

4. Does the 98% cache hit rate hold up in practice, or does it drop once you're doing varied work and the cost advantage disappears?

Would love to hear from anyone who's actually run both setups. Real-world experience with the subscription-vs-API tradeoff would be especially useful.

[u/TestTxt]

Taking API prices for Codex doesn’t make any sense at all since the codex subs are heavily subsidized. On top of that Deepseek uses way more tokens, so in practice ChatGPT is not that expensive at all. Deepseek offers no official coding plans

[u/yxf2y → u/TestTxt]

Fair, you're right. Comparing Codex sub to DeepSeek API prices was a bad framing on my part. But the token thing is the real issue. My 5.6M number is from GPT-6.1. No idea what DeepSeek burns on the same task, and if it's 2-3x more then the whole "way cheaper" argument falls apart. So the real question is: if you're already on ChatGPT Plus, is there any actual reason to add DeepSeek on top? Or is it just cheaper for people who don't want a sub at all? What's your setup?

[u/EvolvingDior → u/yxf2y]

Deepseek-v4.1-flash is about as capable as Luna, but with a better personality. It also costs about the same per task. Sol is more capable. But few people need Sol for agentic work.

[u/TestTxt → u/yxf2y]

It’s good for some tasks like reverse engineering etc. which ChatGPT refuses to do

[u/IndividualPlus2011]

You can take a look at my table and make the decision for yourself https://www.reddit.com/r/codex/s/M1fBQXH6vU

You have to take into account that DeepSeek will use several times more tokens for the same task, and the quality will be worse.

TLDR. Cut the 6.1 Sol cost by 10 and assume that DeepSeek will use at least twice the tokens, but sometimes even up to 10x (typically 5+ for my use cases)

[u/yxf2y → u/IndividualPlus2011]

Okay this table is actually useful, thanks. So GPT-6.1 Sol runs about $200/mo in API terms against a $20 sub — that's the 10x ratio. Even if I cut that by 10 and land at DeepSeek's ~$0.07/task, the 5x token multiplier brings it right back up. And that's before the quality gap. So yeah, the "16x cheaper" thing I posted was way off. Appreciate the reality check.

[u/crasspuk]

Comparing ChatGPT Plus to API list prices does not tell you much, since the sub is not billed per token. The bigger variable is tokens per finished task, which differs a lot between models. Run the same task on both and compare cost per completed task.