user23699: I'm ~1900 rapid on Lichess. As Black, I like to play this defense against 1.e4 (picked up from watching Hikaru's streams):
[FEN ""]
1.e4 g6 2.d4 Bg7 3.Nc3 c6 4.Nf3 d5 (4.f4) (4.Be3)

Are there any books or online resources available for learning more about this defense and the strategic ideas behind it?

user23596: This video gives some insight into black's ideas
Chess Opening for Black: The Gurgenidze System
a well known idea is to exchange the c8 Bishop with the help of h5 when white goes for f4 and then e5 after black plays d5
[FEN ""]
1.e4 g6 2.d4 Bg7 3.Nc3 c6 4.f4 d5 5.e5 h5 6.Nf3 Bg4 7. Be3 Nh6 8. h3 Bxf3 9. Qxf3 Nf5 10. Bf2 h4 11. Bd3 e6  

The g7 bishop will re-route to e7 giving extra support on h4. You could even delay playing Bg7 early so you can play Be7 straightaway without losing tempi.

23699: <p>I'm ~1900 rapid on Lichess. As Black, I like to play this defense against <code>1.e4</code> (picked up from watching Hikaru's streams):</p>
<pre><code>[FEN &quot;&quot;]
1.e4 g6 2.d4 Bg7 3.Nc3 c6 4.Nf3 d5 (4.f4) (4.Be3)
</code></pre>
<p>Are there any books or online resources available for learning more about this defense and the strategic ideas behind it?</p>
 23596: <p>This video gives some insight into black's ideas<br />
<a href="https://www.youtube.com/watch?v=r07qvSgTOQ8" rel="nofollow noreferrer">Chess Opening for Black: The Gurgenidze System</a></p>
<p>a well known idea is to exchange the c8 Bishop with the help of h5 when white goes for f4 and then e5 after black plays d5</p>
<pre><code>[FEN &quot;&quot;]
1.e4 g6 2.d4 Bg7 3.Nc3 c6 4.f4 d5 5.e5 h5 6.Nf3 Bg4 7. Be3 Nh6 8. h3 Bxf3 9. Qxf3 Nf5 10. Bf2 h4 11. Bd3 e6  
</code></pre>
<p>The g7 bishop will re-route to e7 giving extra support on h4. You could even delay playing Bg7 early so you can play Be7 straightaway without losing tempi.</p>
