ActionResult<IEnumerable<Model>> vs IActionResult in ASP.NET Core WebAPI

Hello,

What is the difference between ActionResult<IEnumerable<SpeakerModel>> vs IActionResult ?

I ran both of them and got the same result.

       public IActionResult GetAll()
       {
            return Ok(SpeakersList);
       }

          [HttpGet]
          public ActionResult<IEnumerable<SpeakerModel>> GetAll()
          {
               return Ok(SpeakersList);
          }