Updated September 10, 2026: DeepSeek V4.1 Flash is released. Use
deepseek-flash. The old Flash aliases now route to this version;deepseek-v4-prois scheduled to switch on September 14 at 04:00 UTC. Direct DeepSeek API usage has separate billing.
After the announced alias switch, comparing these two aliases may compare the same backend. Verify the returned model before describing the run as a Pro-versus-Flash comparison.
Decide what would justify an upgrade
Pick one defect that fails a test, one missing test and one documentation change. Define allowed files and acceptance checks before starting. Run Flash and Pro from separate copies of the same baseline with identical instructions, tool access and timeout. Record the alias and date; do not assume a dated release suffix is an API ID.
Retain every attempt
For each run save the input revision, model, runtime, prompt, final diff, check output, failure category and manual correction notes. Include unsuccessful runs when calculating cost per accepted change. An empty cost cell means unknown; zero is valid only when measured as zero.
Make a bounded decision
An upgrade is useful if it improves the result you need within your budget, including review effort. Three public exercises are an onboarding check, not a blind benchmark or a statistically reliable product ranking. Use previously unseen repository tasks before making a broader performance claim.
Start with the downloadable first task, record attempts in the CSV templates, and check the current API status before rerunning.