Bug?: New FSRS 6 parameters not appearing after reoptimizing

jhdv · July 30, 2025, 9:47pm

A few days ago, I updated to Anki 25.07 to try out the new FSRS 6. So after updating, I went to my decks settings and clicked optimize. However, I noticed that after optimizing, there where still only 19 parameters even though FSRS 6 now has 21. Also, restarting Anki did not make the parameters appear. What I needed to do is to first reset the parameters and then optimize for the additional parameters to be computed. I am unsure whether the other 19 parameters where proper FSRS 6 parameters. I had this issue with both of my decks.

Is this intended behaviour? If so, where is it comunicated that this is a step that needs to be taken?

A_Blokee · July 30, 2025, 11:20pm

Disable the health check tick box and do you get the text “Your FSRS parameters are already optimal“?

A_Blokee · July 31, 2025, 12:18am

I made a pr in case it is this.

github.com/ankitects/anki

Feat/Show health check and already optimal at the same time

main ← Luc-Mcgrady:change-health-message-logic

opened 11:59PM - 30 Jul 25 UTC

Luc-Mcgrady

+18 -13

The current implementation where the health check overrides the already optimal …message seems liable to cause some confusion: https://forums.ankiweb.net/t/bug-new-fsrs-6-parameters-not-appearing-after-reoptimizing/64921/2 <img width="384" height="153" alt="image" src="https://github.com/user-attachments/assets/94cf93aa-ff02-488b-90ee-134186fdf845" />

jhdv · July 31, 2025, 6:03pm

Yes I do. When I do tick the box, this text does not appear.

However, this changes nothing about the missing parameters, so I think this is unrelated to the issue?

A_Blokee · July 31, 2025, 6:40pm

This means that FSRS 5 is outperforming FSRS 6 for that preset. If you want to use FSRS 6 anyway, clear your existing parameters before hitting optimize.

jhdv · July 31, 2025, 6:51pm

Oh, I didn’t know that Anki only updates the FSRS version when it actually performs better. So, if I already updated to FSRS 6, can I just copy the old FSRS 5 parameters into the field and then Anki will revert to FSRS 5?

A_Blokee · July 31, 2025, 8:03pm

Yep .

jhdv · July 31, 2025, 8:06pm

Awesome. Well then, thanks for helping!

dae · August 4, 2025, 6:30am

@L.M.Sherlock could you confirm that’s actually the case? My assumption was that if a lower param count is detected (= older fsrs), the missing params and just filled in prior to feeding it into fsrs6?

L.M.Sherlock · August 4, 2025, 6:52am

Here are some cases that the old parameters are used:

github.com/ankitects/anki

rslib/src/scheduler/fsrs/params.rs

2b55882cc


      
          let fsrs_items = items.len() as u32;
          if fsrs_items == 0 {
              return Ok(ComputeFsrsParamsResponse {
                  params: current_params.to_vec(),
                  fsrs_items,
                  health_check_passed: None,
              });
          }

github.com/ankitects/anki

rslib/src/scheduler/fsrs/params.rs

2b55882cc


      
          let mut params = fsrs.compute_parameters(input.clone())?;
          progress_thread.join().ok();
          if let Ok(current_fsrs) = FSRS::new(Some(current_params)) {
              let current_log_loss = current_fsrs.evaluate(items.clone(), |_| true)?.log_loss;
              let optimized_fsrs = FSRS::new(Some(&params))?;
              let optimized_log_loss = optimized_fsrs.evaluate(items.clone(), |_| true)?.log_loss;
              if current_log_loss <= optimized_log_loss {
                  if num_of_relearning_steps <= 1 {
                      params = current_params.to_vec();
                  } else {
                      let memory_state = MemoryState {
                          stability: 1.0,
                          difficulty: 1.0,
                      };
          
                      let s_fail = current_fsrs.next_states(Some(memory_state), 0.9, 2)?.again;
                      let mut s_short_term = s_fail.memory;
          
                      for _ in 0..num_of_relearning_steps {
                          s_short_term = current_fsrs

This file has been truncated. show original

dae · August 4, 2025, 7:42am

My understanding is as follows: “No, Anki doesn’t revert to FSRS5. It fills in the missing parameters, and uses those with the FSRS6 algorithm.”

@L.M.Sherlock can you confirm that’s correct?

L.M.Sherlock · August 4, 2025, 7:54am

Yes. Anki will use FSRS6 with the FSRS5’s parameters in this case.

vaibhav · August 4, 2025, 8:32am

The missing parameters are replaced by the values that were hardcoded in FSRS-5. So, it is equivalent to using FSRS-5.

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Bug?: New FSRS 6 parameters not appearing after reoptimizing

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